Efficient Analysis of Shielding Effectiveness of Metallic Rectangular Enclosures Using Unconditionally Stable Time-Domain Integral Equations

This paper proposes an efficient modeling technique for transient electromagnetic analysis of a rectangular metallic enclosure with multiple apertures, using the surface equivalent principle (SEP) and integral equations. The SEP is used to replace the apertures by perfect electric conductor surfaces while introducing appropriate magnetic current densities on both sides of the apertures. As a result, the problem is reduced to two independent regions. The first region is outside the enclosure for which the free-space Green's function with the aid of image theory can be used to obtain the total fields in it. The second region is the inside of the enclosure and a closed-form expression is then derived for its time-domain dyadic Green's function. Finally, the governing time-domain magnetic field integral equation (TD-MFIE) for the structure is derived by enforcing the continuity of the tangential magnetic field at the apertures. To eliminate the late time instabilities in solving the resultant TD-MFIE, an unconditionally stable marching-on-in degree scheme is used. A new accelerated algorithm is proposed for the internal problem that relies on the separation of time and space in the cavity Green's function. The validity of the proposed method is confirmed by comparing the simulation results of several case studies with those obtained using the frequency-domain methods and CST microwave studio.